This invention relates to a carburization of ferrous alloys, and more particularly, to a method of carburizing a low alloy steel having a carbon content of less than 0.5 percent to produce spheroidal or spherical carbides in a case of the steel.
Heretofore, it has been necessary to include more than 2.4% chromium in the alloy steel to produce spheroidal or spherical carbides by any of conventional carburizing processes.
It has been well known that spheroidal or spherical carbides may be randomly produced in austenite grain boundaries or within austenite grains by carburizing an alloy steel containing more than 2.4% chromium in a carburizing atmosphere having a carbon potential of more than Acm. However, for alloy steels containing less than 2% chromium widely used for practical application, carbides formation within austenite grains may hardly be occurred and net shape or massive carbides are produced in austenite grain boundaries even if the steels are subjected to a carburizing process in a carburizing atmosphere having a carbon potential of more than Acm.
A carburized steel having net shape or massive carbides in austenite grain boundaries are likely to produce quenching cracks and grinding cracks and have a poor pitting resistance or endurance limit of pitting. It is hardly possible to convert these net shape or massive carbides produced in grain boundaries into spheroidal or spherical carbides.